Secondary batteries, such as lead-acid batteries, use a liquid electrolyte which tends to stratify when cycled. The stratification occurs during charge and recharge, affects cell performance and reduces battery life. Additionally, ambient heat and efficient distribution of the internally generated heat are problems where the electrolyte is essentially stagnant. A simple and cost effective technique for gently circulating the electrolyte and increasing the heat transfer efficiency of such a battery has still not been made available.
The prior art is replete with examples of various devices used to circulate electrolyte in secondary batteries or otherwise prevent stratification. U.S. Pat. No. 916,320 issued on Mar. 23, 1909 to H. F. Joel illustrates a technique of tapering a center electrode in a circular battery and slanting the outer conical electrode relative to the separators such that the gas collecting on either side of the separator moves upward and accumulates in ever narrowing passageways, forcing electrolyte as bubbles up through orifices at the top and then over to the outside of the outer electrode where it moves downward. According to the patentee this draws the denser electrolyte from the bottom of the battery. U.S. Pat. No. 2,584,117 issued on Dec. 28, 1949 also recognized the problem and proposed the use of an air blown device to aerate the electrolyte to alter the density thereof to create circulation. Still another U.S. Pat. No. 4,283,467 issued Aug. 11, 1981 to Gutlich, et.al. discloses a device that also utilizes gas to alter electrolyte density. U.S. Pat. No. 4,308,322 issued Dec. 29, 1981 describes a pump within the battery comprising a gas collecting hood and passageways which utilize the generated gas to carry electrolyte as bubbles to the passageways, thus inducing circulation. Another design to reduce stratifiration is disclosed in U.S. Pat. No. 4,619,875 issued to D. W. Stahura, et.al. in which the separator has a plurality of laterally extending concave ribs on the surface thereof that act to trap the more dense electrolyte.
U.S. Pat. No. 529,199 issued Nov. 13, 1894, to Schoop describes the use of a mechanism in a battery which utilizes disturbances occurring in the liquid electrolyte due to movement of the battery to create hydrostatic heads. Once the head is created, the mechanism permits dissipation of the head into currents of electrolyte, thus decreasing stratification and increasing the heat transfer efficiency of the battery. The various mechanisms of the Schoop patent used to create circulation, however, are expensive to manufacture, difficult to assemble, and often require moving parts.